The invention relates to a method of observing the aim or effect of a laser beam on a target.
Lasers have already found wide utility in industrial and medical operations, and new uses are continually being discovered. In many of these industrial and medical operations, however, the intensity of the laser beam which is required for the operation is harmful to observe. Government regulation of exposure to laser radiation by the U.S. Bureau of Radiological Health is one indication of the harm to an observer which can result from observing laser beams and the need to protect the observer from the laser beam.
The danger to the observer from the laser beam is readily understood in many industrial and medical operations in which the intended effect of the laser beam on the target is destructive. For example, carbon dioxide lasers have found medical utility because the laser wavelength is readily absorbed by water and thus can readily remove water-containing tissue. The desired tissue-removing function, however, also indicates that the aim and effect of the laser on the tissue which is to be removed cannot be observed while the laser beam is present because the portion of the laser beam which is reflected or scattered by the target would harm the observer's eye in the same way as it desireably removes tissue at the target.
Many laser devices therefore have a shutter which blocks the observer's view of the target while the laser beam is present to protect the observer. One such shutter arrangement, for example, is disclosed in the assignee's U.S. Pat. No. 3,659,613. The shutter in this patent is a rotating, segmented chopper disc having alternate segments which reflect the laser to the target and block the observer's view of the target and segments which allow observation of the target. The view-blocking segments of the chopper disc are rotated into operative position in synchronism with laser pulses to block each pulse but the pulses are provided at a frequency higher than is observable so that the appearance to the observer through the alternate segments is of a continuous view of the target. In fact, however, the actual aim and effect of the laser beam while the laser beam is present cannot be observed because the chopper disc shields the observer from the laser beam while the laser beam is present. Other shutter arrangements which are not synchronized to non-observable laser pulse frequencies are known, but even further impair the observer's view of the aim and effect of the laser.
Shutter arrangements which prevent the laser beam from being reflected or scattered from the target to the observer present still a further problem. Inasmuch as the laser light is blocked from the observer for protection, another source of light for observing the target while the laser beam is not present must be provided. Ambient light on the target is sometimes available to readily solve this problem, but in other industrial or medical operations the target may be shielded from ambient light to thus require a source of light other than the laser beam for observing the target. For example, laser beams have been directed inside human body cavities with fiber optics or articulated guides. The body about the target then shields the target from ambient light so that, when a shutter blocks the laser light, further arrangements for illuminating the target for observation have to be provided. One such target-illuminating arrangement is suggested in the assignee's beforementioned U.S. Pat. No. 3,659,613, and another which is specifically directed to endoscopically illuminating a target inside a body is disclosed in the assignee's further U.S. Pat. No. 3,906,953. The apparatus for illuminating the laser targets for observation disclosed in these patents could be eliminated, however, if the light provided by the laser beam could also be used for observing the target without harm to the observer.